1. Field of the Invention
The present invention relates to an optical fiber connecting part and an optical module using the same, for electrically and mechanically connecting an optical fiber to a photoelectric conversion module, on which a light emitting device or light receiving device is mounted on a substrate.
2. Description of the Related Art
In recent years, techniques of performing high-speed transmission of digital signal of large capacity in order to transmit photographic data or moving image data of large capacity at high speed between devices such as computer and liquid-crystal display. For transmitting the digital signal of large capacity at high speed, an optical interconnection system using an optical fiber as transmission path between the devices such as computer, liquid-crystal display, video camera, data recorder has been developed in these days.
As the optical interconnection system, for example, Japanese Patent Laid-Open No. 2006-310197 (JP-A 2006-310197) discloses a system for connecting between devices by means of an optical cable, which comprises a connector including a photoelectric conversion module inside and is connected to an end of a complex cable comprising an optical fiber and a signal line (metal wire).
In such optical fiber, an end face of the optical fiber in the complex cable is connected to an optical device such as light emitting device or light receiving device which is mounted on the substrate in the photoelectric conversion module via an optical fiber connecting part at a connecting portion between the complex cable and the connector. For example, Japanese Patent Laid-Open No. 2007-256372 (JP-A 2007-256372) discloses such technique.
Conventionally, as the optical fiber, for example, a singe-core optical fiber 244 with a structure shown in FIG. 24A, and a multi-core optical fiber (tape-like optical fiber) 246 with a structure shown in FIG. 24B have been used. The single-core optical fiber 244 comprises a core 240, a clad 241, a low Young modulus layer (inner coating layer) 242 having Young modulus of 10 MPa or less and provided around the clad 241, and a high Young modulus layer (outer coating layer) 243 having Young modulus of 100 MPa or more and provided around the low Young modulus layer 242. The multi-core optical fiber 246 comprises a plurality of the single-core optical fibers 244 that are aligned in one column (geometrically in parallel), and the high Young modulus layer (coating layer) 245 having Young modulus of 100 MPa or more and coating the aligned single-core optical fibers 244.
The single-core optical fiber 244 or the multi-core optical fiber 246 is bonded and coupled at its end part to a ferrule (optical fiber connecting part) to provide a connector, and used for an optical module in which a tip end of the connector is optically connected to an optical device, other optical fiber or the like.
For forming a connector from the conventional optical fiber, an optical fiber should be inserted into the ferrule. As shown in FIGS. 25A to 25C, a conventional ferrule 250 comprises an optical fiber insertion hole 251 which has an inner diameter greater than an outer diameter of the single-core optical fiber 244 including the inner and outer coating layers 242, 243 and is provided on a side of one end of the ferrule 250, and a light input/output bore 253, which has an inner diameter substantially corresponding to an outer diameter of the clad 241 of the single-core optical fiber 244 (i.e. slightly greater than the outer diameter of the clad 241), and inputs and outputs a light at an end face of another end part 252 of the ferrule 250, in which the optical fiber insertion hole 251 communicates with the light input/output bore 253. This optical fiber insertion hole 251 and the light input/output bore 253 are concentric.
FIG. 26 shows the single-core optical fiber 244 connected and bonded to the ferrule 250 as shown in FIG. 25A to 25C. An inner structure of the ferrule 250 is as follows. An optical fiber comprising only the core 240 and the clad 241, i.e. the single-core optical fiber 244 from which the inner and outer coating layers 242, 243 (the low Young modulus layer 242 and the high Young modulus layer 243 as shown in FIG. 24A) are removed, is inserted into the light input/output bore 253 provided on the another end part 252 of the ferrule 250, and is fixed with an adhesive 260. Thereafter, a light input and output end face 261 of the ferrule 250 is polished. As to a cross section of the ferrule 250, the ferrule 250 may have a rectangular cross section in addition to a circular cross section as shown in FIG. 25A.
The multi-core optical fiber 246 has a structure similar to the structure of the single-core optical fiber 244. The high Young modulus layer 245 which collectively coats the multi-core optical fiber 246 is removed, and respective cores 240 are separated from each other. Thereafter, the multi-core optical fiber 246 is inserted into the ferrule 250, in which bores of the number corresponding to the number of the single-core optical fibers 244 are formed, and terminal-processed similarly to the structure shown in FIG. 26.